The present invention relates to a contact piece for air-cooled transformers constructed of an insulating mass and provided with conductive lines in the interior thereof for providing switching connections to the delta connection of the three windings on a three-legged core transformer. In accordance with the contact piece of the present invention, the center connections are attached at the longitudinal sides of the contact piece opposite one another and are disposed in the area of the ends of the outside connections. The present invention is particularly suitable for use in transformers made of casting resin.
A contact strip of a contact piece of the initially mentioned type is generally known from the description in German Utility Patent No. 1,971,623. This known contact strip consists of an elongated, block-shaped body of synthetic resin in which three electric contacts are disposed on the two long, narrow sides. Such connecting blocks must be premanufactured serially in the sizes needed for adaptation to various transformer dimensions and must be maintained in stock. Thus, the problem of utilizing conventional contact pieces for air-cooled transformers is that such conventional contact pieces cannot be produced for any given standardized transformer type or size and thus cannot be produced in only one single size. Therefore, since the contact piece of the present invention can be manufactured in one size which would fit typical transformer sizes, the cost and stock inventory problems typically encountered with conventional contact pieces are alleviated.
This problem is solved by the contact piece according to the present invention in that at least in the case of one pair of outside connections disposed at one end of the contact piece, the connecting contacts are accessible from the direction of the vertical sides of the contact piece in the mounted position so that they are in the general area of the relative front sides thereof. As a result of this relative positioning of the connecting contacts, it is possible that one may dispense with laterally projecting contacts accessible only from the direction of the horizontal sides in the mounted position and advantageous results are achieved which are believed to have been heretofore unattainable with conventional contact pieces.
The individual connecting elements may be attached to the outside connecting contacts of the present invention and thus may be connected with the respective connecting contacts of the transformer windings.
The contact piece of the present invention is preferably symmetrical. In other words, two outside connections have been provided in the contact piece of the present invention at each side thereof. For such functions, the connecting contacts of the outside connections are preferably counter sunk into the front sides of the contact piece. The connecting contacts may also be in the form of brackets, eyes or wire hooks which will project more or less from the width of the insulating mass of the contact piece depending upon the specific mechanical and/or structural requirements.
The shape of the contact piece according to the present invention preferably deviates from the box or rectangular shape typically associated with conventional contact pieces. In a preferred embodiment of the present invention, the contact piece in top view has a narrowed cross section at least in the area of the middle connections as compared to the cross-sectional areas of the contact piece in the vicinity of each of the front sides. The contact piece therefore has the general appearance of an X- or an hour-glass like shape as viewed from above.
Because of this particular configuration of the contact piece, considerable quantities of material may be saved since the distance or creepage path between the blank surfaces of the connecting contacts of the middle connections disposed in the cross sectional constriction is essentially equal to the distance or the creepage path between the blank surfaces of the two connecting contacts in the area of the front sides.
Finally, the advantages of a contact piece according to the present invention also extend to the shaping of the customarily necessary protective cap. The latter is preferably shaped as an essentially U-shaped box in cross section which bridges the extreme horizontal distance between the connecting elements. The cap preferably defines three bores on its front side separated from one another by an equal distance and being disposed equally distant from the edge of the protective cap.
With the contact piece according to the present invention, assembly and installation work may be accomplished in a very short time thereby saving labor costs. Additionally, the contact piece may be produced at a more reasonable cost than the customary cuboid-shaped contact piece since one single contact piece will be sufficient for practically all transformer dimensions.
The body of the contact piece constructed of an insulating mass having the conductive lines inserted therein may be produced according to any known casting processes, for example, injection molding, die casting with cold-hardening casting resin in the open casting process or with hot-hardening casting resin in a vacuum. It is also possible to provide the connecting piece of the present invention in two parts, namely, a cover and a bottom, in which corresponding grooves are provided in which the conductive lines are placed.
Additional advantages and characteristics of the present invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiment which follows.